1. Field of the Invention
The present invention relates generally to a touch panel, and more particularly, to a touch panel having low resistance and superior transmittance.
2. Description of the Prior Art
Conventional touch panels include resistive, capacitive, infrared (IR) and acoustic touch panels, among others. The resistive and capacitive touch panels are widely used while the capacitive touch panels draw more and more attention because of advantages of humanized operational mode provided by its characteristic of multi-touch.
FIG. 1A is a top plan view of a portion of a conventional touch panel. FIG. 1B is a cross-sectional view taken along abbreviated line A-A′ of FIG. 1. Please refer to both FIG. 1A and FIG. 1B. The touch panel 100 is exemplarily a capacitive touch panel and includes a substrate 110, a plurality of first sensing strings 120 and a plurality of second sensing strings 130. The first sensing strings 120 are disposed on the substrate 110 and parallel to each other. Each of the first sensing string 120 includes a plurality of first sensing pads 122 and a plurality of first connecting lines. The first connecting lines 124 are parallel to a first direction D1 and electrically connected to the first sensing pads 122 in series. The second sensing strings 130 are disposed on the substrate 110 and parallel to each other. Each of the second sensing string 130 includes a plurality of second sensing pads 132 and a plurality of second connecting lines 134. The second connecting lines 134 are parallel to a second direction D2 and electrically connected to the second sensing pads 132 in series. Dielectric patterns 126 are formed between the first connecting lines 124 and the second connecting lines 134 for electrically isolating the first connecting lines 124 from the second connecting lines 134.
For example, a signal is sequentially transmitted to each of the first and second sensing strings 120, 130. When the touch panel 100 is touched by a user's finger, a capacitance is generated at the touched point by the first sensing pad 122, the second sensing pad 132 and the finger. Thus signal changes are caused in the first sensing string 120 and the second sensing string 130. Accordingly, the touch point is recognized by detecting the signal changes in the first sensing string 120 and the second sensing string 130.
When the size of the touch panel 100 is increased, the length of the sensing strings of the touch panel 100 is consequently increased. Therefore, a line resistance of the first sensing strings 120 along with the first direction D1, or a line resistance of the second sensing strings 130 along with the second direction D2 is increased. Consequently the sensitivity of the touch panel 100 is deteriorated. In particularly, the first sensing pads 122 and the second sensing pads 132 include transparent conductive material such as indium tin oxide (ITO).
Please refer to FIG. 1C, which is an illustration of a correlation diagram of a thickness of the ITO corresponding to the sheet resistance and transmittance. The thickness of the ITO is substantially inversely proportional to the resistance. Therefore, the prior art has developed a method to increase the thickness of first sensing pads 122 and the second sensing pads 132 of the touch panel 100 in order to reduce the resistance. However, when increasing the thickness of the first sensing pads 122 and the second sensing pads 132, the transmittance of the touch panel 100 is deteriorated as shown in FIG. 1C.
Accordingly, China Patent Application Number 200710138674 and US Patent Application Publication Number US20090085891 respectively provide a method for reducing the resistance of the touch panel. However, it is found that a layout provided by China Patent Application Number 200710138674 is limited by the transmittance of the touch panel and its provided manufacturing process is relatively complicated. US Patent Application Publication Number US20090085891 reduction in resistance is of little value, but the downsides of such design applies the use of both sides driving method and which, as consequence, causes adding more electrode strings plus enlarging the peripheral region.
There is therefore a continuous need to develop the touch panel 100 having improved sensitivity and high transmittance.